It is conventional to monitor automatic industrial production processes. For instance, in synthetic yarn false twisting machines in which endless threads are subjected to a false twisting operation for the purpose of imparting to them characteristics similar to the irregular structure of natural fibres, it is necessary and conducive to obtaining desirable results, in performing the false twisting operation that the thread or yarn move at a tension maintained within a predetermined range. Yarn tension above or below the predetermined range will likely result in a useless product. Hence, the tension of a moving yarn is routinely monitored for purposes of controlling and, in case of undesirable deviations, adjusting the operation of the machine. U.S. Pat. No 4 720,702 issued Jan. 19, 1988 to Gerhard Martens and assigned to the present assignee discloses a method and apparatus for monitoring the tension of a moving yarn which in case of an error signal of predetermined duration provides for the generation of visual or audible alarms and for the cutting of the yarn. An error signal is generated, whenever the tension goes beyond an upper or lower limit. The disclosure of U.S. Pat. No. 4,720 702 is expressly incorporated herein by reference.
Modern textile machines, including synthetic yarn false twisting machines, as a rule are provided with a great many operating positions, sometimes as many as 216, divided into 18 work stations of 12 positions each. Each of these positions may be provided with a heater for raising the temperature of the yarn before it enters the false twisting apparatus and with appropriate feed rolls for moving the thread at a predetermined tension from a supply thereof to a bobbin. In addition, each working position may be provided with an electromechanically actuated facility for cutting the thread in response to a signal indicating that thread tension is outside of a desired range. The electromechanical cutting fixture may be controlled by circuitry deriving readings of the tension of each thread by way of sensors.
Providing separate control circuits and memories for each one of the working positions would, of course, be unduly complex, and the expense would be prohibitive.
It is, therefore, an object of the present invention to provide for a method and apparatus for monitoring the tension of a plurality of threads moving in as many working positions and for storing error signals in a memory of limited capacity for the purpose of analyzing the cause of any incorrect tension and/or of controlling the operation of the working position as a function of thread tension.
It is a more general object of the invention to provide a method of storing a plurality of error signals generated by a plurality of sources in orderly fashion in a memory of limited capacity.
Yet another object of the invention is to provide a method of storing in a memory error signals from a plurality of sources in which earlier error signals may be eliminated in favour of later derived signals.
Still another object of the invention is to provide for a method of storing, in orderly fashion, error signals from a plurality of working stations of a synthetic yarn false twisting machine, in memory space ordinarily insufficient for the number of signals.
It is also an object of the invention to provide a method of storing error signals in such a way that signals derived from one working position may at least in part override earlier stored error signals from another working position.